Dazomet (Tetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazine-2-thione) is a nonselective fumigant with several uses. Fumigants form gasses after application that have biocidal activity. When dazomet is applied, it is quickly broken down into several active degradation products. The major degradation product formed by dazomet is methyl isothiocyanate (MITC). MITC is highly volatile and is responsible for the fumigant properties of dazomet. In the soil, dazomet exhibits fungicidal, herbicidal and nematicidal properties. Unlike other soil fumigants, dazomet is applied as a dry granule and incorporated into the soil or applied to the soil surface and watered into the soil to activate it. Dazomet is also registered as an algaecidal, bacteriocidal, fungicidal, microbicidal, and mildewcidal agent for use during the production of pulp and paper, treatment for coatings, adhesives, epoxy flooring compounds, slurries, and high viscous suspensions, biocidal treatments in petroleum operations and recirculating water cooling systems and as a remedial treatment of wooden utility structures.
Long-term test results have demonstrated the excellent efficacy of dazomet as a wood pole fumigant. The addition of an accelerant, such as copper naphthenate, increases the release of fumigant early in the treating cycle, thus eliminating concerns from earlier testing that the product was not breaking down fast enough to deliver a lethal dose to the inhabiting fungi.
Diffusible preservatives, often containing boron or fluoride compounds, come in a wide spectrum of different forms, including powders, pastes, gels, thickened solutions, and solid rods. Some diffusible preservative treatments take the form of boron or boron-copper mixtures which are melted and molded into rods. Other diffusible preservative treatments are boron-containing pastes which can be applied to the wooden structure to be preserved and then formed into a desired shape and left to solidify before application.
Several products using dazomet for remedial treatment of wooden utility poles are commercially available. Granular fumigants, such as Osmose's DuraFume®, contain a crystallized solid dazomet fumigant that decomposes to produce MITC. Application of granular fumigants in the field, however, is cumbersome and inefficient. Like liquid fumigants, granular fumigants must be poured into treatment holes pre-drilled from above, and are also subject to spilling and difficulties in accurately measuring the proper dosage of dazomet to be applied. Granular fumigants are also subject to clumping and unwanted dust production. Addition of accelerants, such as copper naphthenate or copper sulfate to granular dazomet in a utility pole leads to inefficient and sub-optimal distribution of the accelerant throughout the dazomet granules.
Although boron- and fluoride-based rods overcome the disadvantages of granular compositions and have been commercially developed, the formulation of dazomet into compressed solid forms has not succeeded in producing a product with sufficient hardness, friability and performance necessary for field use. Oregon State University's Utility Pole Research Cooperative (UPRC) tested a fumigant “rod” containing dazomet that was similar to boron-containing diffusible preservative rods. The UPRC “rods” were prepared by wetting powdered dazomet with water followed by compression into pellets. Water, however, triggers dazomet decomposition to produce the active MITC biocide, during manufacturing. MITC generation prior to application raises is inefficient and potentially hazardous. The UPRC pellets exhibited poor friability and hardness which is unsuitable for commercial applications and normal handling and applications in the field.
There has long been a need in the utilities industry for an alternative to granular dazomet formulations that could possibly eliminate some of the undesirable handling characterizes of a granular formulation. Although a dazomet rod product could fill the market void as a substitute for granular systems, no serious efforts to commercialize them have taken place.
The difficulties in formulating a dazomet rod suitable for commercial applications has resulted in the development of several alternatives to a compressed dazomet rod. In one case, dazomet is packaged into preformed tubes. For example, Super-Fume Tubes have been developed, based on the same effective and safe granular formula that is applied from jugs (HDPE/HDPP Containers). The tubes use a perforated or gas-permeable outermost packaging material to contain a pre-set dose of the granular dazomet product. Another alternative to granular dazomet is Osmose's MITC-FUME®. This product consists of an aluminum tube filled with solid 97% MITC (instead of dazomet) and capped with an air-tight seal.
Compositions of dazomet suitable for formation of solid dazomet bodies, such as rods, that have properties (such as hardness and friability) suitable for use as commercial wood preservative for the internal remedial treatment of wood are disclosed herein. Methods of producing such dazomet compositions and solid bodies and methods for their use in the remedial treatment of wood utility structures, such as wood utility poles, are also disclosed.